<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        button {
            cursor: pointer;
        }
    </style>
</head>
<body>
    <button>按钮1</button>
    <button>按钮2</button>
    <button>按钮3</button>
    <button>按钮4</button>
    <button>按钮5</button>

    <script>
        var but = document.querySelectorAll('button');
        for(var i = 0; i < but.length; i++){ 
            but[i].onclick = function (){                
                for (var j = 0; j < but.length; j++) {
                        but[j].style.backgroundColor = '';
                }
                this.style.backgroundColor = 'red';
            }
        }
    </script>
</body>
</html>